Pre-press or off-press color proofing is used by printers to simulate the images that will be produced by a printing process. Pre-press color proofing systems include overlay proofing systems and surprint, or single sheet, systems. Both overlay proofs and surprint proofs are commonly used as “contract proofs.” A contract proof serves as a promise by the printer to a customer that a proofed image will be duplicated by the printing process when the press prints are made. Therefore, the printer desires to have proofs that can most accurately predict the image that will be reproduced by the press prints. The need for accurate proofs is especially critical where custom colors are employed in the printing process.
In an overlay proof, each printing color is generally segregated onto a separate transparent sheet or film, known as an overlay. The number of overlays in an overlay proof will usually equal the number of inks that will be used in the printing process. The individual overlays are assembled in registration to make the overlay proof, which is viewed as a composite against an appropriate background (e.g., an opaque reflective white sheet), to predict the appearance of a printed image. In an overlay proof the individual overlays remain separable and can be viewed separately or superimposed. A number of commercial overlay proofing systems are described in detail in “Principles of Color Proofing,” by Michael H. Bruno, GAMA Communications (Salem, N.H. 1986); see especially Chapter V: “Off-Press Color Proofing System-Overlay” (pp 133-146).
Each overlay is made from an overlay proofing film. A traditional overlay proofing film construction includes a substrate and a layer of colored photosensitive material. Photosensitive proofing films which can be used in image-reproduction processes are well-known in the graphics arts industry. Proofing films are usually exposed to radiation through an image-bearing transparency, such as a color-separation transparency, to reproduce the image onto the proofing film. After imagewise exposure, the photosensitive layer may be developed to produce an imaged overlay. Developing is generally done by washout of soluble image areas (e.g., non-exposed areas in a negative-acting transparency), by peeling apart, by toning with a colorant, or combinations of these techniques.
Digital color proofs have been made by directly transferring a colored substance from a “donor” sheet to a “receptor” sheet using a rastering laser beam or an array of laser beams. A donor sheet covered with a layer of ink of a particular stock color, such as cyan, magenta, yellow or black (commonly known as the “CMYK” color system), is juxtaposed with the receptor film, with the ink-side in between. The ink contains an infrared (“IR”)-absorbing material. The donor film is exposed to an IR radiation pattern
Generally, overlay proofing films are made in large volume and are pre-colored at a factory. Thus, in the production of an overlay proof, the end user is generally limited to those stock colors that are available from the manufacturer. Because of the cost of manufacturing, storing, and distributing overlay proofing film materials, necessarily only a limited range of colors will be available from a manufacturer. The limited range of colors provided by the manufacturer is adequate for many purposes, but does not enable an end user to accurately mimic difficult-to-match colors. For example, many fluorescent or metallic colors are virtually impossible to mimic using the standard process colors cyan, magenta, yellow and black. Even for colors that are theoretically reproducible by standard process colors, the tones of the colors so produced are often not sufficiently precise for specialized applications of the customers.
Methods for making overlay proofs including a custom color are known. U.S. Pat. Nos. 5,001,037 and 5,122,437 to Matthews, et al. report a process for preparing a multi-layered, multi-colored overlay proof comprising at least one precolored overlay image and at least one toned image. The process includes the steps of exposing a non-colored tonable photosensitive overlay element, developing the exposed overlay element, and toning the developed photosensitive element using a toner. U.S. Pat. No. 5,232,814 to Graves, et al. reports color proofing elements for producing images in non-standard colors, and in particular metallic-appearing images. The proofing elements include a support layer and require two layers of pigment.
The invention disclosed herein is aimed at providing a method and system for processing radiation-sensitive patterning compositions substantially without the drawbacks of the conventional approaches.